Separation of wax from hydrocarbon oils



Nov. 6, 1934.. R. E. MANLr-:Y

SEPARATION OF WAX FROM HYDROCARBON OILS Filed April 20, 1931 NNI Q Km.RN.

/NVENTOR ,Ll/5 A TTORNEY Patented Nov.- 6, 1934 UNITED STATES PATENToFFIcE SEPARATION OF WAX FROM HYDROCARBON OILS Robert E. Manley, PortArthur, Tex., assignor to The Texas Company, New York, N. Y., acorporation of Delaware Application April 20, 1931, Serial No. 531,648

l Claim.

This invention relates to the separation or extraction of `paraiiin waxfrom hydrocarbon oils, and more 'particularly to an improved4 propertiesofA dissolving all the hydrocarbonsA contained therein atielevatedtemperature and having a selective solvent action between the liquidhydrocarbons and solid hydrocarbons at relatively low temperatures,chilling the liquid solution to a point where the solid hydrocarbonsseparate out, then filtering the chilled solution to remove-the liquidhydrocarbons in solution from the separated solid hydrocarbons andwashing the resulting filter cake of separated solid hydrocarbons, insitu, with` cold solvent liquid to remove entrained or adhering oil.

In my prior application, Serial No. 233,565, Afiled November 16, 1927, Ihave describeda process' for dewaxing hydrocarbon oils by ltration of achilled mixture of solvent and oil in the presence of a filter-aidmaterial and wherein the resulting cake of solid hydrocarbons andlter-aid material is subjected to,washing by forcing an oil solventthrough the material deposited on the lter atk such temperature that nosubstantial quantity of the waxy constituents may be dissolved therein,whereby a substantially complete separation of voil from .the waxy F5constitutents isfobtaineli. y

-My present invention comprises an improvement to the method of dewaxingoils disclosed in the aforesaid application, and has particularreferenceto the treatment of the slack wax 40 cake to eiect complete removal ofthe adhering and retained oil, and also produce substantially oil-freeslack wax which is entirely satisfactory for sweating for the productionof high melting -point wax. The invention has particular reference tothe so-called solvent type of dewaxing process wherein, for example, thewax-bearing oil is mixed withlacetone and benzol in such a. ratio toeach other and to the said fraction that the acetone and benzol togetherat temperatures of approximately 100 F. have substantially completesolventaction on the waxbearing oil and at temperatures of 5 F. andbelow, have substantially complete solvent action on the liquidhydrocarbons but substantially no solvent action on the -solidhydrocarbons in said fraction, and upon removal of the solidhydrocarbons and the acetone and benzol, such oil has a cold testsubstantially the same as the temperature of the mixture at the time ofthe removal of the solid`hydrocarbons, and following which the mixtureis cooled to a temperature at which substantially all of the solidhydrocarbons are precipitatedand the cooled mixture then subjected toltration toI separate the solid hydrocarbons so precipitated. E

The iilter cake of slack Wax or petrolatum formed in the filtrationmethods of dewaxing Wax-bearing hydrocarbon oils usually containssubstantial proportions of 'liquid hydrocarbons which are not -onlyvaluable as lubricating oil but also whenallowed to remain even infairly small amounts in the Wax cake inhibit and pre- `vent thesatisfactory sweating of the wax cake.

The complete removalof this adhering oil, particularly in the case ofwax filter cakes formed in the dewaxing of hydrocarbon oils by means ofa selective solvent such as acetone and ben'zol,

and wherethe resulting cake does not contain lter aid material, hasnever been realized heretofore.L As is usual in filtering operations ofthis type when a lter cake of desired thickness hasbeen built upion theltering surfaces, it is customary to stop the iiow \of liquid into thefilter and displace the contents of the lter shell, either-by drainingout or by blowingback with gas or air and then subjecting the cake towashing with asuitable-washing liquids However, during the draining ofthe lter or blowing back of the-lter shell contents, and which includesthe body oiliquid immediately adjacent the cake, substantial portions ofthe cakemay fall completely away from the iiltering surface, or the:cake may develop cracks so that during the subsequent cake washing stepthe'` washing liquid short circuits through the cracks in the cake 'y orthrough those portions of the-filtering ,sur-

li'aces vfrom which the cake has fallen; thus militating against theuniform'andeiiective washing.

of the filter cake.

thesolvent and dissolved oil while depositing the solid hydrocarbonsonthev ltering surface in the form of a cake.

As soon' 'as a lter cake of desired thickness has been obtained theintro- I stopped and .the introduction to the filter of a solvent washliquid is immediately started without a cessation of 'flow of liquidthrough the filter cake Yand filtering surfaces. 'I'he change in liquidow from solvent and dissolved hydrocarbon liquid to pure solvent washingliquid is effected in such a manner as to maintain a continual plusliquid pressure on the filter cake during the final stages of filtrationas well as throughout the washing period. In this way there is a body ofliquid continually in contact with the entire surface of. the cakeexerting a positive pressure thereover to facilitate its completeadherence to the filtering surfaceso that it does not become partiallydislodged therefrom prior to or develop cracks during thefinitial stagesof the washing period and, consequently, sinceshort circuiting of thesolvent wash liquid is thus prevented, the filter cake is subjected to acomplete and effective washing action, thereby resulting in theobtaining of a substantially oilefree wax cake.

Reference may be'made to the accompanying drawing which illustratesapparatus suitable for practicing the method of my invention.

This apparatus may comprise a charging tank 1 from which the dilutewax-bearing mixture is introduced to a chiller 2 wherein it may bechilled to a temperature of around 0 F. or below. From the chiller, theoil is conducted' through a pipe 3 having a valve 4 into the interior'of a filter 5. if'

The filter 5 is advantageously of the rotating leaf type and adapted forpressure filtration. It comprises an insulated shell containing afiltering element comprising a series of hollow leaves 6 supported on,vand integral with, a hollow rotating shaft '7.' In operation, thesolids are deposited* on the exterior 4surfaces of the hollowleaves`while the filtrate passes therethrough into the interior of theleaves. Fromi the interior of eachleaf, the filtrate flows into thehollow shaft 'l from which it is discharged through a filter valve 8. l

From the valve 8, the filtrate is discharged through a pipe' 9 having avalve 10..

Solvent "liquid for washing the cake is con-j ducted from a tank 11through a pipe 12, having a valve 13, into the interior of the filter 5.This wash solvent, together with the oil displacedfrom the filter andfilter cakes, is 'removed from the filter through the hollow shaft rI ina manner similar tothat of the filtrate already described.v However, thewash liquidfmay be removed from the valve. 8 through a separate pipe v14 having a valve 15.

4`lDuring filtration the filter shell is maintained -tance to flow offluid through the cake, the pressure within the filter shell,asindicated on- 'a pressure gauge 16, alsoincreases, reaching a givenmaximum point when a cake of desired thickness has been formed.

At this point, the valve 4 is gradually closed l while -the valve 13 is'simultaneously open so as to maintain a substantially constant inflow offluid tothe interior of the filter shell and thus continually maintain aplus-pressure therewithin.

The inflowing wash solvent liquid mingles with the liquid contents ofthe filter shell, and is displaced through the lter cakes into thehollow shaft 7, from which it is discharged from the filter. The flow ofwash solvent into the filter is, continued until all the oil remainingin the filter shell and adhering to the 'cakes is displaced. Thereupon,the valve 13 is closed, and cold gas introduced to the lter through avalve 17 for the purpose of displacing the bulk of the remaining liquidcontents of the ltery through the leaves and into the hollow shaft 7.The remaining portion of the liquid contents of the filter shell may bedrawn off from the lter shell through a drain valve 18. Following this,the filter cake is removed from the filter leaves inthe usual manner byapplying to the interior of the leaves a reverse flow gas pressure. Thewax cake which thus aceumulates in the bottom ofthe shell is dischargedtherefrom through a valve 19.

As an' example for, the purpose of illustrating one mode of operation, Idissolve 1,000 gallons of wax bearing mineral-oil at a temperature of 90`F. in a mixture of 1,110 gallons of acetone and 1,890 gallons. ofbenzoland cool the solution 1n vthe chiller 2 to ,-10* F. to effectprecipitation of f the solid hydrocarbons. The cooled mixture ofVdissolved oil and solid matter suspended gtherein is introduced tofilter press 5, advantageously of the rotating leaf type, wherein thesolvent and dissolvedv liquid hydrocarbons are removed and a filter cakeof slack wax of desired thickcake and filtering surfaces while thefiltering element is kept in drotation, thus displacing the filteringmixture of solvent, dissolved oil and solid hydrocarbons from thefiltery and also displacing the liquid hydrocarbons fromthe cake itself.The Ywashing is-kept up until a sample of the solvent wash liquidAexhibits a compara.'- tive absence "of dissolved liquid hydrocarbons,indicating that the retained oil has been substantially completelyremoved from the filter i cake. The introduction of solvent wash isthen( stopped whereupon a cool gas is admitted through the valve 17 tothe filter to displace the greater portion of the solvent liquidretained in the filter cake and after which the filter cake is ,removedfr om the lter.

The washed cake may then be transferred to a still wherein the solventis removed by evap'ofration and recovered for further use and the.solvent free wax is run to sweat pans wherein it y be sweated in theusual manner to a desired melting point or to produce wax fractions ofdifferent melting points.

All or a portion ofthe wash solvent liquor accumulated during thewashing of the filter cake may be used as the original solvent formixing with fresh wax bearing oil which is to undergo treatment. On theother hand, all or a portion of it may be run in with the filtrate andsubjected to distillation therewith to remove the solventliquidandfurnish additional low cold test oil since the ,wash liquid maycontain substantial amounts of such oil dissolved therein.

The portion of the wash liquor diverted back to the filtrate isdependent upon the quantity of oil or liquid hydrocarbon dissolvedtherein, the wash liquor or solvent initially passing through the press,particularly during the oil displacement period, being quite rich inAdissolved oil and becoming progressively leaner as washing continues,nally reaching a point where it contains substantially no dissolved oil,and at which point it 'may advantageously be I diverted Without furthertreatment for use in the dissolving of fresh Wax bearing oil.

While in the above example I have described a dewaxing operation whereinthe wax-bearing mineral oil has been mixed with a selective solventconsisting of suitable proportions of acetone and benzol, it iscontemplated that the invention is equally applicable to` dewaxingoperations wherein other solvents, suchas petroleum naphtha, forexample,y may be employed.

'Ihe invention is not limited to the treatment of a mineral oil such asgiven in the example herein, but is adapted to the treatment of otherwax containing fractions of precipitates obtained from crude oils andmay, for example, embrace the treatment of solid yhydrocarbons containedin a slack Wax produced in the manufacture of low cold test lubricatingoils, and which material is an equivalent of the stock referred to inthe example. Thus, while the example describedl advantageously `setsforth one modeof operation, the invention is not restricted to anyparticular set of operating conditions such as that of temperature,etc., as therein described and it'is, therefore, contemplated that manymodications and variations of the invention, as hereinbefore set forth,may be made without departing from the spirit and scope thereof, andtherefore only such limitations should be imposed as are indicated inthe appended claim.

I claim:

In the process of manufacturing lubricating oil from wax-bearing mineraloil comprising mixing the oil with a solvent comprising acetone andbenzol mixed in substantial proportions, chilling the resulting mixtureto a temperature of 0 F. or lower to eiIect precipitation of solidhydrocarbons and introducing the chilled mixture to, pressurelteringmeans to remove the solvent and liquid hydrocarbons and form aillter cake of solid hydrocarbons, the steps comprising introducingacetone and benzol mixed in substantially the same proportions andchilled to a temperature of 0 F. or below to the filtering meanssimultaneously with the cessation of flow of filtering mixture thereto,whereby Ithe lter is maintained full of liquid and a plus liquidpressure is continuously maintained upon the lter cake throughoutfiltration and the subsequent cake washing step, thereby preventingfracturing or dislodgment of the cake, continuing the ilow of saidsolvent through the cake, in situ, to remove adhering and entrainedliquid hydrocarbons therefrom, and while uninterruptedly continuing thepositive pressure within the filter forcing a cool gas through thewashed cake to remove retained solvent liquid.

ROBERT E. MANLEY.

